1. Field of the Invention
The present invention relates to a polarizer that converts circularly polarized light into linearly polarized light in a visible light range, and more particularly relates to the polarizer and method of making the polarizer which has a fine line therein that enables the polarizer to serve as a high transmittance polarizer for use in a display, such as a computer display.
2. Discussion of the Background
Several examples of conventional polarizer, and the problems associated therewith are descried below.
A first conventional method of forming method a polarizer and a polarizing plate is explained in Japanese Laid Open Patent Application No. 01-93702. In this document a polarizing plate is made according to a straight-forward manufacturing process, where the plate has excellent optical properties. The polarizing plate includes many rod elements arranged on a surface of a substrate in a predetermined direction and affixed thereto. The respective rod elements are made of fine ferromagnetic particles.
As identified by the present inventors, an uneven distribution of the respective elements in the polarizing layer is large, as is an unevenness of the rod element material itself. With respect to the material, it is necessary that the material exhibit a large light absorption and refractive index. However, such materials are not preferable at this point in time, for various reasons.
A second conventional polarizer is a wire grid polarizer that is described on Page 103 in "Physics of a Man of Today--Light and Magnetism", by Katsuaki Satoh of Tokyo Agriculture and Industry University, 1988. This paper describes a polarizer that functions on light having a longer wavelength than 2.5 .mu.m. In this polarizer, a line of gold or aluminum is formed on a transparent substrate (silver bromide or polyethylene etc.) at a fine interval therein. In this case, when the interval of the line is d and the wavelength is .lambda., with respect to light having a wavelength .lambda.&gt;&gt;d, a transmission light becomes almost completely linearly polarized, with a vibrational surface that is vertical with respect to the line. For a middle infrared ray (i.e., .lambda.=2.5 .mu.m to 25 .mu.m), the gold line is formed at an interval of d=0.3 .mu.m on the substrate of silver bromide. For a long infrared ray (i.e., .lambda.=16 .mu.m to 100 .mu.m), the aluminum line is formed at an interval of d=0.7 .mu.m on the substrate of polyethylene. The respective degrees of polarization are generally thought to be about 97%.
As identified by the present inventors, a problem with this conventional apparatus is that the apparatus works on infrared rays having a relatively long wavelength, but does not function on rays in the visible light range. Moreover, in this wire method, a width of the line cannot be narrowed, such as to 500 .ANG. or less.
POLAR CORE is a conventional product offered by Corning Company and is a glass material that has a polarization property owing to an arrangement of metallic silver that is extended in one direction. The material has advantages in that it is heat resistant, moisture resistant, chemical resistant, and resistant to damage by a laser, unlike conventional polarizers made of organic materials. This product is mainly for use on infrared rays, however, under special specification conditions the material may be used on visible light.
As identified by the present inventors, a limitation with POLAR CORE is that when it is used for visible light, the material has a brown-colored outward appearance. Thus, the material is not suitable for use in a display device because it is dark and does not have the needed contrast, as is the case with conventional polarizers made of organic materials. Further, the price of the material is high and it is difficult to make large units with this material. Moreover, a light transmittance characteristic of this material is between 400 nm to 800 nm (when a thickness is 2 mm), and thus, it is not enough.
A group of Tohoku University has described a micro wire array that has a surface of aluminum that becomes oxidized in an anode and becomes alumina, and a fine hole is formed therein. Ni or Cu etc. are inserted into the fine hole, and thereby the polarizer for the infrared ray is formed.
As identified by the present inventors, insufficient evidence is present on the characteristics of its light transmission, however, transmittance in the infrared ray range, which is a main utility range, is 85%, a low value. This group makes the polarizer by inserting a metallic particle layer in an island-like form, between glass layers so as to extend the metallic particle layer. However, a degree of polarization is not enough in the visible light range and thus it is also only suitable for use in long wavelengths in the infrared ray spectrum.
A laminating type polarizer is reported by Professor Shoujiro Kawakami of Electricity and Communication Laboratory in Tohoku University. The polarizer is for use in the visible light range and uses Ge (germanium) of 60 .ANG. to 80 .ANG. in thickness and SiO.sub.2 of 1 .mu.m in thickness alternately laminated so as to create a composite thickness in the neighborhood of 60 .mu.m. A performance index .alpha.TE/.alpha.TM (ratio of exhaustion constant of a TE wave and a TM wave) which is measured in the wavelength of 0.6 .mu.m, is nearly 400, and the exhaustion ratio which is measured in the wavelength of 0.8 .mu.m is 35 dB, which are adequate for visible light.
However, as identified by the present inventors, since the polarizer is formed by a sputtering method, a thickness of only 50 .mu.m to 100 .mu.m, at most, is formed. This thin film on the substrate is sliced in 3 .mu.m to 35 .mu.m in thickness and then used. The device is used as mounted to a light sensing system or a light wave guide device etc. A similar device that operates for a wave length of 850 nm or more is produced by the similar producing method and is sold as a product name of LAMI POLE by Sumitomo Osaka Cement Company. However, this method cannot be formed into a large size area.
The inventors' previous patent documents describe a technique in which the polarizer is formed by dispersing a metal or semiconductor particle of 100 .ANG. or less in an organic solvent, and coating it on a transparent substrate in straight line form, and heating (burning) the same so as to form the polarizer.
On the other hand, the present invention is a method for forming the polarizer by general lithography techniques, and relates to a basic structure (a fine line being formed on one transparent supporting body), that improves the polarizer described in the previous patent documents. The present method for forming the polarizer involves making the fine line thinner, an improving the aspect ratio (ratio between height and width of the fine line) by making the aspect ratio larger so as to improve performance.